NERC National Capability of the Plymouth Marine Laboratory and Marine Biological Association

WCO Benthic survey

As part of the Western Channel Observatory, the PML benthic survey is an ongoing ecological time-series aimed at capturing the natural temporal and spatial variability of the marine ecosystems encompassed by the Plymouth Sound and contiguous coastal waters. Initiated in 2008 and supported for the last three years as part of the Oceans 2025 Project (NERC), the survey has been aggregated by the Western Channel Observatory, due to the uniqueness and comprehensiveness of the datasets collected, which are aimed primarily at the training and further development of ecosystem models at PML.

Bimonthly sampling has been undertaken at a variety of sites within the Plymouth Sound and contiguous coastal waters, to cover a diversity of habitats and to account for physical, biological and chemical parameters. In this way, every sampling point enables an insight into the different levels of complexity of these ecosystems, the biodiversity and the ecosystem processes it sustains. In parallel, the long-term time-series will enable ecologists and modellers to better grasp the spatial and temporal variation of these ecosystems, and use this to forecast future change of global oceans.

The four sites presently covered by the Survey - L4, Rame Mud, Cawsand Bay and Jennycliff Bay - have contrasting combinations of depth, sediment type and level of exposure. Cawsand and Jennycliff represent shallow habitats (approx. 10 m deep), sheltered from the prevailing south westerly winds, but have different sediment types (Jennycliff being very muddy and Cawsand being sandier). L4 and Rame Mud are exposed sites with a depth of approximately 50 m, with sediments ranging from mud to sand.

Water profiles of suspended particulate matter, chlorophyll, alkalinity, nutrients (nitrate, nitrite, ammonia, silicate and phosphate), temperature, dissolved oxygen and salinity as well as primary production data have been collected at these stations and continue to be monitored at L4. The diversity and abundance of macrofauna, meiofauna and bacterial communities within the sediment are also being studied in parallel to a range of sediment parameters such as sheer stress, granulometry, redox, CHN and steroid analysis. The reproductive stages of selected macrofauna species are also being determined through histology. As important processes in the marine nitrogen cycle since 2009 bimonthly estimates of anammox and denitrification rates have also been monitored, as have nutrient fluxes between the sediment and the water column. The monitoring of three new parameters has been incorporated into the survey in 2011 - nitrous oxide and methane (greenhouse gases),and bioturbation (the collective infaunal activities that lead to sediment particle movement) – and are further enriching the comprehensiveness of the long-term time-series with regards to the assessment of marine ecosystem processes, now and in the future.

Bioturbation assessment using 2D particle tracer methods. Images captured using time-lapse photography under UV lighting. Sediment core collected at Cawsand Bay, where a fluorescent green tracer layer has been added to the surface on recovery to the lab. The tracer can be seen being incorporated into the sediment over time, by various infaunal organisms - e.g. brittle stars and polychaetes - that compose the benthic community at this site. Bioturbation is quantified as the change in the biodiffusion coefficient over the six day incubation.